Caption: On the left is a composite image of Abell 85 made from X-rays from NASA's Chandra X-ray Observatory and optical light from the Sloan Digital Sky Survey. This galaxy cluster is one of 86 observed with Chandra to trace how dark energy has stifled the growth of these massive structures over the last 7 billion years. Galaxy clusters are the largest collapsed objects in the Universe and are ideal for studying the properties of dark energy across the Universe. The illustration on the right shows snapshots from a simulation representing the growth of cosmic structures when the Universe was 0.9 billion, 3.2 billion, and 13.7 billion years old.